Battery bank question and solar power question?

Hey Shoe, yes, it's possible, and lots of people are doing it right now, including me. We live in a home that has been powered by the wind and sun for 13 years now. The show you're watching, "The Colony," is interesting, but their technical grasp is pretty thin on renewable energy. A car battery is poorly designed for storing energy. They have porous plates like sponges that increase the surface area between the acid and lead for very high current short blasts of electricity, like you might need to start a car. Then they ride around all day charging very slowly. It's why they don't generally last more than 4 years or so.

We had a system with 20 golf cart batteries, which are about the same size as a large car battery. One golf cart battery holds 1.3 kilowatt-hours of electricity (kWh). Our home has a refrigerator, deep freeze, laundry machines, coffeemaker, TV, and other normal household stuff. It is only 1100 square feet, so fairly small, and all the lighting and appliances are high efficiency. Still we need about 7 kWh per day including the well pump. Our solar array is 1.4 kilo watts, (kw) and our wind turbine is very small, about the size of a large ceiling fan, it is 1 kw. It is really just enough to run the entire home most of the year, in the spring we come up a little short and have to buy some power from the utility, so my electric bills over a year are usually less than $10 per month, I would say we are providing about 90% of our homes usage. If I increased the array size to 1.8 kw that would probably make us entirely self sufficient, as long as we continue to burn wood for most of our heat and so on.

The Colony throws things like "a 100 car battery bank" and "15 panels" around because they don't realize that those numbers don't mean anything. Car batteries come in many sizes and voltages, panels come in all ranges of sizes. It's like saying I have a dozen vehicles, can I move 50 tons of laundry soap with them. What type of vehicles? How much space will 50 tons need? Easy to make a TV program when you don't bother getting into the details.

There are some places to get the info you want, I'll list some sources below, but you're forgetting the best place, the library. The internet does not have any card cataloging system, so it's no surprise when you use google to find something obscure like solar power, you end up all over the map. If you found one good book in the library on solar powered homes, there would be a dozen others on the same shelf, that's how they are organized. Try your local library's own website for starters, then check these out below. Take care Shoe, Rudydoo

A typical car starter battery is 65 Ah at 12 V which is 780 Wh but lead acid batteries do not like deep discharges, there are deep discharge versions but all lead acid batteries have their expected life rated at only a 20% discharge. Granted in an apocalyptic scenario, the survivors could dump out the acid into a container, file down the plates, maybe replace a few and pour the electrolyte back in. However, to keep with maximum lifespan, you would not want to draw more than 20% of the capacity per day, fortunately, designing only for a 20% draw results in 4 to 5 days of cloudy day capacity hence you design for 156 Wh per battery. However, lead acid batteries are 95% efficient on discharge so you can only count on 148.2 Wh which for 100 batteries is 14,820 Wh which over a 24 hour period gives you 617 watts if you drew power continuously. Since you would most likely be using the battery as little as possible, this could last a long time. Unfortunately, lead acid batteries are only 50% efficient at charging so to replenish a 20% diurnal draw in a typical six hours of usable sunlight ( solar insolation for southern US states ), you would need 5,200 watts of solar panels, about 520 of the typical 2x4 foot 100 watt panels. Surely large enough to attract cannibals from miles around in the setting of "The Colony"

Note that lead acid batteries are rated for 800 cycles so after two years, they would have to be reconditioned by pouring out the electrolytes, filing the plates down, cannibalizing a few batteries for spare plates and reassembling. Survivors would likely eventually suffer acid damage from all the reconditioning especially if they couldn't find protective safety gear. I would try to find Nickel Iron batteries from old fork lifts if I were them, they last forever.

Note "The Colony" is a 2013 Canadian movie so it's only a year old.

I assume by "car battery" your mean a starter battery. A started battery will not last long at all. What you need is a RV batter or deep cycle battery. We accidentally had a starter batter in our RV and the light would dim within minutes of stopping the engine. When we switched to an RV battery of the same size the lights lasted all night.

Anyway, if 20 batteries last a certain time then 100 will last 5 times as long, because 20 * 5 = 100. S0 if 20 batteries last 3 to 7 days, then 100 of them will last 15 to 35 days, because 3*5=15 and 7*5=35.

Solar power is not so different than generator power. YOu need to know basic electricity. Watts = Amps * Volts. Solar panels are rated by watts and volts, Battery capacity is rated by amp hours meaning how many amps they can supply for how many hours. Then you multiply by battery voltage to get watts. But there is a lot more to it. It is really a semester class at a community college (at least) to get up to speed on it. Or maybe a high school year of physics class. At least the part about electricity.

There is a step-by-step video guide online right now that can show you how to reduce your power bill by making your own solar panels.


Take a look at it: http://tinyurl.com/Earth4EnergyRew


Why pay thousands of dollars for solar energy ($27,000 average cost) when you can build your own solar panel system for just a fraction of the retail cost. You can build a single solar panel or you can build an entire array of panels to power your whole house.

Some people are saving 50% on their power bill, some people are reducing their bill to nothing. But what’s most impressive is that just by following these instructions some are even making the power company pay them!

There are lots (well, at least one) of online calculators that will tell you how many batteries and panels you need to run various things for so many days. One I've seen was Carmanah Power. Yes, it would work with enough batteries and panels. Car batteries might not be the best for storage, but they will work, though they might die faster than in a car. Deep-discharge batteries are better. With a lot of old batteries from different cars all connected, it would probably be better to use a battery management system rather than just straight parallel, that way a faulty battery could not short out the bank and explode, and partly-dead ones could still be used without compromising the total performance. Post-apocalypse, you just threaten to shoot the guy in charge if the electricity stops working :-7 and let him manage them.

I don't have any data, but I suspect that while your solar panels would last 20 years, the car batteries would gradually die so that after about 5 years most would be useless. It would also be more efficient to burn stuff for hot water, or use a solar oven, than use PV cells and batteries, at least with current cells